05-05-13: UnsoundSensitivity, defined as the sound pressure level (SPL) generated by the speaker at a given distance, in response to a given voltage at its input terminals, at a given frequency, is what it is for a given speaker.
Al, the wouldn't sensitivity of the speaker vary along with the impedance?
If the impedance of the speaker varies widely as a function of frequency, and if the speaker is driven by a tube amplifier having significant output impedance, then the voltage that appears at the input terminals of the speaker, which will be essentially the same as the amplifier's OUTPUT voltage, will vary significantly as a function of frequency, for a given INPUT voltage to the amplifier.
If the same speaker is driven by a solid state amplifier having near zero output impedance, then the voltage that appears at the input terminals of the speaker will NOT vary significantly as a function of frequency, for a given INPUT voltage to the amplifier.
What matters is minimizing the variation of SPL, as a function of frequency, for a given INPUT voltage to the amplifier. Which of those two scenarios will produce the best results in that respect depends on the design of the particular speaker, and what kind of amplifier the designer envisioned it being used with.
Deadlyvj, thanks for providing the interesting link. A bottom line summary seems to me to be contained in this quote:
Due to voltage driving, the sonic performance of virtually all loudspeaker systems is severely impaired by the diverse electromotive forces (see above) induced in the voice coil motor corrupting the ideal behaviour of the amplifier interface....I think that commenting on that intelligently would require both study of the details that are contained in his book, and more knowledge of speaker design than I possess. But his thesis, as I see it, does not change the fact that if a speaker has wide variations of impedance as a function of frequency, it is likely to perform best with an amplifier having whatever kind of output impedance the designer envisioned it being used with.
The effect is not unknown and can be traced down, but Meriläinen strongly feels that the noise mechanisms related to traditional voltage driving have not been adequately addressed, not in the literature, nor in practice.
No amplifier can remove the internal EMF voltage components at the driver motor, but their diverse effects on the speaker/amplifier interface and hence, on the sound quality, can be diminished with a sufficiently high source impedance.
Best regards,
-- Al